In well bore drilling situations that use a drilling rig, a drilling fluid circulation system circulates (or pumps) drilling fluid (for example, drilling mud) with one or more mud pumps. For example, the drilling fluid circulation system can move drilling mud down into the well bore through special pipe (referred to in the art as drill pipe), and drill collars which are connected to the drill sting. The fluid exits through ports (jets) in the drill bit, picking up cuttings and carrying the cuttings up the annulus of the well bore. The mud pump can take suction from mud tanks and can pump mud out discharge piping, up the stand pipe, through rotary hoses, through Kelly or top drive unit, and into a central bore of the drill pipe, drill collars, and bit. Mud and cuttings return to the surface up annulus. At the surface, the mud and cuttings leave the well bore through an outlet, and can be sent to a cuttings removal system via mud return line. At the end of the return lines, mud and cutting can be flowed onto a vibrating screen known in the art as a Shale Shaker. Finer solids can be removed by a sand trap. The mud may be treated with chemicals stored in a chemical tank and can then be provided into the mud tank, where the process can be repeated.
The drilling fluid circulation system delivers large volumes of mud flow under pressure for drilling rig operations. For example, the circulation system can deliver the mud to the drill stem to flow down the string of drill pipe and out through the drill bit appended to the lower end of the drill stem. In addition to cooling the drill bit, the mud hydraulically washes away the face of the well bore through a set of openings in the drill bit. The mud additionally washes away debris, rock chips, and cuttings, which are generated as the drill bit advances. The circulation system can flow the mud in an annular space on the outside of the drill stem and on the interior of the open hole formed by the drilling process. In this manner, the circulation system can flow the mud through the drill bit and out of the well bore.
The mud flows through the drill stem and the annular space at a sufficient velocity to move debris, chips and cuttings, which are heavier than the mud, to the surface. The velocity of the mud should also be sufficient to cool the drill bit. The wellhead pressures at the pump are sufficiently high to flow the mud at the desired velocity and also to overcome substantial flow pressure resistance along the flow path. In some situations, the circulation system can flow the mud through the drill bit and the well bore at high volumetric flow rates (for example, 500 to 1,000 gallons per minute) and at pressures as high as 5,000 PSI. If drilling fluid flows into the well bore and up the annulus or inside the drill pipe due to an imbalance in drilling mud pressure, then a phenomenon known as kick can result. If the well is not shut in, a kick can escalate into a blowout when the formation fluids reach the surface.
Like reference numbers and designations in the various drawings indicate like elements.